Treatment of case-hardening baths



Patented Dec. 9, 1924,

UNITED STATES roam w. snmnn, crass-romrmmsvnvmn.

maximum or case-Emma Barns,

To all whom it may Be it known that I, Pon'rna W. slim,

" residing at Easton, in the county of Horthampton, State of Pennsylvania, have invented certain new and useful Improvements in Treatment of Case-Hardening Baths; and

1 MI do hereby-declare the following to be a full, clear, andexact description of the ins vention, such as. will enableothersskilled in the art to which it appertains to make and e use the same.

" similar compounds and mixtures which This invention relates to. molten baths for case hardening steel and has among ts objects the renewal of the case-hardening ac- 15 used, orabused for some time.

tivity of such baths after they have been In my United States Patents No. 1,279,457 and ,No. 1,27 9,458, I -have described molten baths containing such mixtures as calcium chloride and sodium chloride; potass1um chloride and sodium chloride; and other after being subjected to theiaction of calcium cyanamide immersed therein, acqulre case-hardeningpropertiea f i I I find that after a case hardeningqbath of the character described has been in use for a considerable of time, especially under crude operating. conditions, the bath gradually. loses its power of acquiring full case-hardening 'propertiesi through the ac tion o calciumj' cyanamide*-,thereonas ,referred to above. "'yf'l his 'loss in th power to acquire case-hardening properties 1 quently hereinafter referred to ashes of case-hardening activity or simply asloss of activity) is sometimes augmented by long continued use of the bath on a largeproduction 'scale,, particularly when the articles being case-hardened are coated;with scale or, when cast iron pots are used tocontain' the" melt; Also I have found .that'trouble" this source is jfrequentlyjjaoc'entuated-when baths containing calcium ichloi-ideJjliav' 0t been thoroughly-dried, jwhenthey' 11 vs taken up water by long standing under e posure to" atmosp eric moisture; or mois'ture= from other 'sourcesll ..Further'm'ore,- Ia have found that this 1058i]! case-hardening activity seems to increasewith thelamount ofr,

lime, iron and other impurities,'including silica, that. are taken up' by the bath from extraneous sources and particularly from the calcium cyanam'ide lumps which are suspended in the jbathfor the purpose ofim- Application fled June 29, 1922., Serial nofwnais.

parting case-hardening activity thereto in accordance with the methods described in my prior patents referred to above. 1 c

When used baths or deterioratedbaths which have lost more or less of their casehardening activity, are subjected to further action of calciumcyanamide to impart caseh'ardening properties in the usual manner, I find thatt-he lumps of calcium cyanamide or coked calcium cyanamide often become coated to a greater or less degree with a layer of material which ordinarilylhas a I copper colored'appearance and I believe that this coating over the calcium cyanamide has the efiect of impeding the taking up from the calcium cyanamide by the bath ofthose constituents of the calcium cyanamide which impart the ori a1 case-hardening activity to the bath. film of this material also adheres to or deposits on the steel parts im- "mersed in the bath, causing an impediment tocase-h'ardening. The film will-also form on: other infusiblesolids immersed in the bath. 7

' In accordance with the present invention when suchj deteriorated baths with low casehardenin activity are subjected to a treatmentwhich results in the separation from the molten bathof a basic dross relatively hlgh irr-c'alcium 1 iron contentj find that jthe bathagain acguires its full originalac- I'fin that when a-bath treated in ithiszmanner is again'subjected to the action oi fresh calcium'cyan'amide, the separat on, j the' copper colored insoluble compoundzup'bn the surface of the calcium cyanam de no longer takes place to any consider abIeeitent. Furthermore the reactivated bathffrom which the basic dross has been separated, has the power todissolve the cop'- Pet coloredcoating from the surface of cal 'cium cyanamide which has previously been immersed in a deteriorated .or inactive bath;

I, ebasic dross which.results from the treatment of the bath' 'in accordance with my, invention, ordinarily contains .a higher pgrcentage'of calcium and iron than the th after treatment; and I, find also that after the separatiouefthe drossthe calcium content of the bath-gisgconside'rably lower than it was before'fthe :se aration of the dross; Ialso find thatthe asic dross contains a'higher percentage of iron than the bathfrom which-the dross'has been caused to separate; The treated is, as a rule,

very much'whiter than the untreated bath of low activity before the drosshasbeen caused to separate therefrom, and in general the treated bath is in a higher state of purity and more nearly approaches in composition a freshly prepared and unused bath 7 of the character described in my two patents referred to above;

The changes which occur "in a freshly made'ba th with continued use and which result infa deteriorated bath of lowcasehardening activity consist in part, I believe, in thefformation of basic compounds in the bath, particularly basic chlorides such as calcium oxychloride and I conceive that the effect of moisture mentioned above in forming these impurities is that it brings about alimited hydrolysis of certain of the chlorides such as calclum chloride to produce basic chlorides such as calcium oxychloride and a certain amount of hydrobath. I V v As a reagent for bringing about a separachloric acid which is driven ofi, or the re action may sometimes. go further, I believe, to roduce calcium oxide dissolved in the molten bath. Also I conceive that the deleterious effects upon the case-hardening activity of the bath produced by long con-, tinned immersionof the calcium cyanamide are due to a. dissolution of basic calcium compounds or like 'basic compounds from the vcalcium cyanamide by the action of the tion of the basic dross I use preferably a substance capable of mixing, fusing, melt- 1ng,;or.dis solving in the molten bath and wh1ch,jafter it has thus become incorporated in Ythebath reacts with or otherwise'aifects the constituents thereof in such way as to form a basic' dross rich in lime and in-. soluble inithe moltenbath. -Also I prefer to'carry-outthis reactionin such-manner or produce it with a reagent of such character, that the-resulting drossfis not-only/insoluble in the molten ,bathbut is also granular or lumpy in character. so that it'may be readily removed from the molten bath by means {of a suitably preforated ladle.

In the practice of my invention in its pre ferredxform, I employ, asa reagent for I bringing about the separation-of thebasic dross, ordinarf v,metallic aluminum and I prefer toad v e'inetallic aluminum to the bath while it in the molten condition, although. Imay addit in powdered form tothe original bathmixture and also I prefer to use ordinarily only about an ounce of metallic aluminum to a pot containing say about 100 pounds of the molten mixture such as calcium chloride and sodium chlo-" ride. The addition of the metallic aluminum soon causes a noticeable activity or commotion in the bath, followed by the separation of lumps of dross, a part of which floats on top of the. bath, the remainder settling to the bottom. When the bath has been kept at the proper temperature 'While I'do not 'WlSh to restrict the scope of my invention b any unwarranted assumptions as to the exact chemical reactions brought about by the aluminum orequivaot, best by means of a suitlent reagent, nevertheless I am'of the opinion that the metal first reacts'with oxygen or oxide in the bath atthe somewhat/elevated temperature thereof'to produce an oxide of the aluminum and then the ox'ide'thus vformed combines with lime, etc., in the bath to form compounds of higher melting point than that of the bath. As a result of the higher" melting point of the compounds thus formed and'also because of their insolubility in the molten bath, they separate from-the bath in the form of a basic dross.

is not restricted to the employment of metallic aluminum as thereagent in the example described above but I may use any Itiwill be understood that my invention I equivalent reagent fulfilling the requirements already referred to namely that the reagent must be capable of reacting either directly. or indirectly with the excess of lime or calcium oxide" or other objectionable constituents in the bath to' form compounds therewith which arejinsoluble in the molten bath. I Thus in place of metallicaluminum I may use metallic alloys relatively rich in aluminum or I may use metallic magnesium,

or like powerful deoxidizing metals or alloys thereof rich'in these metals. Also I may use in place of metallic aluminum the chloride of aluminum or the chloride.

olff jchromium since these com ounds meet the! q ements referred to a ove, that is "to s'ayit "are capable of reacting in such way astdfl-ifigcttheelimination from the bath of theexeess"; calcium oxide (or calcium oxychloride) or "like objectionable impurities inQthe bath through the-formation of an insolubledross, v I

Other equivalent reagents will the obvious to those skilled :in theart concerned, 1

I claim: I L 1. The method I ingiprqperties'iz to a molten bath of the character described which comprises subjecting the bath to the action of a strongly of imparting case-harden- I deoxidizing metal and then subjecting the bath to the action of calcium cyanamide substantially as described.

2. The'method of imparting case-harden- 5 ing properties to a molten bath of the character described, which comprises subjecting the bath to the action of metallic aluminum and then subjecting the bath to the action of calcium cyanamide substantially as described.

In testimony whereof I affix my signature.

PORTER W. SHKMER. 

